Conventionally, a silicon single crystal is mainly manufactured by the CZ method. In the CZ method, first, silicon polycrystalline raw materials are put into a quartz crucible and heated with a graphite heater to melt the raw materials. A seed crystal attached to a lower end of a superior axis is immersed in the resulting melt and then slowly pulled while rotating the superior axis, thereby growing a silicon single crystal. An apparatus for growing a silicon single crystal in this manner is referred to as a silicon single crystal pulling apparatus.
In the silicon single crystal pulling apparatus, since a melt surface within the quartz crucible sinks with pulling of a silicon single crystal, the crucible is elevated by the decrease in the melt surface to keep height position of the melt surface constant. It is necessary for pulling a silicon single crystal having a certain diameter to control pulling rate of the silicon single crystal and temperature of the melt while measuring the diameter during pulling such that the diameter is kept constant and to elevate the crucible at a predetermined ratio relative to the pulling rate.
In addition, the conventional silicon single crystal pulling apparatus includes a fixed heater, which cannot move during pulling of a silicon single crystal, so that oxygen concentration of the silicon single crystal decreases with the progress of pulling. To inhibit the decrease in oxygen concentration, rotational speed of the crucible is increased, however, this tends to degrade the oxygen concentration distribution in radial direction of the cross section of the silicon single crystal. In view of this, a silicon single crystal pulling apparatus disclosed in Patent Document 1 has configuration in which not only the crucible but also the heater can move vertically, thereby improving the oxygen concentration distribution in axis direction of a single crystal.
A silicon single crystal pulling apparatus disclosed in Patent Document 2 includes a moving mechanism capable of elevating and lowering a shield (heat insulating cylinder). After completion of pulling of a silicon single crystal, the shield is elevated, and then a region below the shield, which has been inside the shield, is exposed to a water cooled chamber to efficiently cool the interior of the water cooled chamber. Thus, this apparatus reduces the time required for cooling the chamber, thereby improving productivity.